What is solvent pop, and what often causes it?

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Solvent pop is tiny bubbles that form in a coating because solvent vapor gets trapped as the finish cures. As the film dries, the solvent wants to escape, but if the layer is too thick, the air is humid, or evaporation happens too quickly, the vapor can’t escape smoothly and pockets of vapor create bubbles that later show up as craters or pimples in the cured finish. This is most often seen when a film is applied thickly, when environmental conditions have high humidity, or when solvent evaporation is rapid due to heat or aggressive drying. To prevent it, apply thinner coats with adequate flash-off time, control the environment (lower humidity if possible, moderate temperature), and use reducers/solvents that suit the film and conditions.